Wedge-Lock System For Injection Molds

ABSTRACT

A wedge-lock system for injection molds, using a protrusion on one side of the mold and a mating opening and sets of wedges which act together upon mold closing to provide and maintain accurate centering of the core and cavity halves in reference to each other, to prevent core shifts and compensate for uneven thermal expansion of mold components.

FIELD OF THE INVENTION

The present invention relates to plastic injection molds, and inparticular to a centering wedge system to maintain concentricity betweencore and cavity halves and achieve consistent wall thickness of themolded parts.

BACKGROUND OF THE INVENTION

A common challenge of injection molds is the difficulty to achieve andmaintain a uniform wall thickness of the molded part while overcomingand compensating for various injection molding processing conditions.Prior art injection molds typically have a core versus cavity lockingsystem, with wedges having various clamp angles such as 7° to 20°angles. While the clamping force of the injection press holds the moldclosed during injection, injection forces sometimes overcome theclamping force, causing the mold to breathe at the parting line. As anexample, a breathing gap of 0.001″-0.007″ at the parting line, combinedwith angles of 7°-20° on wedges, produces gaps of 0.0009″-0.0024″between core and cavity wedges, resulting in loss of concentricity whereone side of the mold half shifts out of center to the opposing side andcauses inconsistent wall thickness of the molded part. A typicalprocedure to restore concentricity is to shim the wedges; this methodhowever is time consuming and offers only temporary results since theprocessing conditions that caused the core verses cavity shifting iscontinuously present. A solution to counter this problem is to usesmaller angles on wedges (3° or 1° or less), but such small angle makesfor difficult control of thermal expansions and tends to cause thewedges to gall and/or seize. Furthermore the tolerances required tobuild a mold and maintain the same mold increases which results in morecost.

Therefore, existing locking systems pose an ongoing challenge to removethe floating effect caused by high injection pressures. A solution isdesired, which allows the locking system to constantly self-adjust inorder to maintain concentricity, while allowing control of thermalexpansions and preventing galling of the wedges ans.

SUMMARY OF THE INVENTION

The present invention is directed towards a wedge-lock system forinjection molds, using sets of wedges which act together upon moldclosing to provide and maintain accurate centering of the core andcavity halves in reference to each other, to prevent core shifts andcompensate for uneven thermal expansion of mold components, whilst usingthe clamping force of the injection press to aid the centering of moldhalves.

In accordance with an aspect of the invention there is provided, a wedgelock system for injection molds comprising a mating core block andcavity block which move between an open position and closed position,and in said closed position molten plastic may be injected between thefaces of said core and cavity blocks to form a plastic injection moldproduct, said wedge lock system comprising: a forward protrusion in thecore block which mates with a corresponding opening in the cavity block,said protrusion having a first lateral side and an opposite angledlateral side; a first cavity wedge, secured to the cavity block withinthe cavity block opening; a core wedge assembly including a core wedgepiece positioned adjacent the first side of the protrusion and beingconnected by compressible attachment means which extends laterallythrough said protrusion to at least one floating puck, said at least onepuck extending laterally outwardly from said angled side of theprotrusion; a second cavity wedge secured to the cavity block having amating angled surface to the angled side of the protrusion, which insaid closed position, engages the angled side of said protrusion andurges said laterally outwardly extending at least one floating puckinwardly to compress said compressible attachment means and thereby urgesaid core wedge piece into firm contact with said first cavity wedge.

In accordance with a further aspect of the invention, there is provideda wedge lock system for injection molds comprising a mating core blockand cavity block which move between an open position and closedposition, and in said closed position molten plastic may be injectedbetween the faces of said core and cavity blocks to form a plasticinjection mold product, said wedge lock system comprising: a wedgecompressibly mounted to the face of said core block or cavity block,biased in a floating position away from said block, said wedge having anangled surface to the direction of movement of the mold machine, saidwedge being compressed against said block as the angled surface of thewedge comes into engagement with a mating angled surface of a wedgesecured to the opposite side of the mold (or with a mating angledsurface of the opposite side of the mold directly), as the moldapproaches the closed position thereby providing enhanced clamping forcein the closed position during plastic injection.

In accordance with a further aspect of the invention, there is provided,a wedge lock system for injection molds comprising a mating core blockand cavity block which move between an open position and closedposition, and in said closed position molten plastic may be injectedbetween the faces of said core and cavity blocks to form a plasticinjection mold product, said wedge lock system comprising: a forwardprotrusion in the core block (or cavity block) which mates with acorresponding opening in the opposite block, said protrusion having afirst angled lateral side and an opposite angled lateral side; a firstopposite block portion, situated opposite said first angled lateral sideof the protrusion having a mating surface to the first angled side ofthe protrusion; a second opposite block portion, situated opposite saidsecond angled lateral side, wherein, in said closed position, said firstand second opposite block portions engage the respective first andsecond angled sides of the protrusions, thereby creating increasedclamping force in the closed position. Wedges may be secured to one orboth sides of the protrusion and/or one or more of the opposite blockportions.

Other advantages, features and characteristics of the present invention,as well as methods of operation and functions of the related elements ofthe structure, and the combination of parts and economies ofmanufacture, will become apparent upon consideration of the followingdetailed description and the appended claims with reference to theaccompanying drawings, the latter being briefly described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary vertical sectional view of an injection mold ofprior art, having a locking system comprising core and cavity wedgeswith a taper between 7° and 20°;

FIG. 2 is an exemplary plan view of the core half of an injection moldhaving a locking system in accordance with an example embodiment of thepresent invention;

FIG. 3 is an exemplary plan view of the cavity half of the injectionmold of FIG. 2;

FIG. 4 is an exemplary vertical sectional view taken along line A-A ofFIG. 2;

FIG. 4A is an exemplary vertical sectional view corresponding to that ofFIG. 4, showing the mold in a partially open position;

FIG. 4B is an exemplary vertical section view similar to that of FIG. 4,showing an alternate embodiment of the invention;

FIG. 5 is a detail showing a comparison between various angles oflocking wedges in accordance with various embodiments of the invention;

FIG. 6 is a spatial view of the mold core half of FIG. 2;

FIG. 7 is a spatial view of the mold cavity half of FIG. 3;

FIG. 8A is an enlarged detail of a cross-section taken along line B-B ofFIG. 7, showing a gap-free design between core block and cavity wedge,having floating core wedges, spring-activated transversally;

FIG. 8B is an enlarged detail of a cross-section taken along line B-B ofFIG. 7, showing a design with gap between core block and cavity wedge,having floating core wedges, spring-activated transversally;

FIG. 9 is an enlarged detail of a cross-section similar with that ofFIG. 8A, but of a first alternate embodiment using floating core wedges,spring-activated transversally and providing roller bearing contactbetween core and cavity wedges.

FIG. 10 is an enlarged detail of a cross-section similar with that ofFIG. 8A, but of a second alternate embodiment using floating corewedges, spring-activated axially.

DETAILED DESCRIPTION OF THE INVENTION

An example embodiment of the invention is described with reference toFIGS. 1 to 7, and in particular the sectional views of FIG. 4 and FIG.4A. A typical injection mold comprises a bottom plate 10, a core block12, a cavity block 14, and a top plate 16. Bottom plate 10 and top plate16 are securely attached to the injection machine platens (not shown),and the mold opening and closing motion is guided by a leader pin system18.

In accordance with an aspect of the invention, core wedges (alsoreferred to as core wedge pieces) 20, together with cavity wedges 22,form the main locking system 24 of the mold. In the embodiment shown,cavity wedges 22 are firmly secured to the cavity block 14 with sockethead cap screws 26 or other suitable means. Core wedges 20 are attachedto but not secured firmly to core block 12, being allowed to float aswill be explained in more detail below. In the embodiment shown, corewedges 20 and cavity wedges 22 have a small taper (0°-3°).

As shown in FIGS. 4 and 4A, core block 12 has protrusions 28 extendingforwardly towards the cavity block 14. Protrusions 28 have a straightface (90°) oriented parallel to the direction of movement of the mold,backing each core wedge 20, and an angled surface with a taper of 3° to20° on the opposite angled lateral side (For example the embodiment ofFIG. 4 shows a 7° taper on this surface). Opposite this taper ofprotrusions 28 is another set of cavity wedges (second cavity wedge) 30,which are firmly secured to the cavity block 14 with socket head capscrews 32 or other suitable means. It should be understood that althougha preferred range of angle is 3° to 20° an angled surface with a taperof less than 3° and more than 20° is contemplated by the invention.

As can be seen in FIGS. 2 and 4, 4A, each core block protrusion 28 isprovided with a pair of compressible spring-loaded pucks 34 which areconnected, through the protrusion to core wedges 20 by way of shoulderbolts 36. The system formed by core wedges 20, spring washers 38 (suchas for example Belleville type), pucks 34 and shoulder bolts 36, hassome degree of floating freedom in core block protrusions 28 when themold is open, along axes of shoulder bolts 36.

When the mold is in open position (such as shown in FIG. 4A),compression means such as spring washers 38 release until the counterbores of pucks 34 come to rest against the heads of shoulder bolts 36.This causes core wedges 20 to be pulled against protrusions 28 as thepucks 34 extend slightly over the angled surfaces of protrusions 28. Asthe mold closes for a new injection cycle, cavity wedges 30 come incontact with pucks 34, causing the pucks to compress spring washers 38and forcing the core wedges 20 into firm contact with cavity wedges 22.The combined effect of the large angle (3° to 20°) of cavity wedges30/pucks 34 and the floating allowance of pucks 34 allows core wedges 20and cavity wedges 22 to engage into firm contact only at the finalmoment of mold closing, thus preventing wear at this interface. Thus,the clamp force of the injection press is applied to the core and cavitywedge interface only in the final moments of mold closing, and is usedto achieve and maintain firm contact between the wedges at all timesduring injection, even if the mold should breathe slightly at theparting line. Furthermore, the small angle between wedges 20 and 22 (3°or less) provides for improved concentricity.

As can be seen in FIG. 5, a 0.007″ gap at the parting line amounts toonly a 0.0004″ gap between wedges having a 3° taper. Therefore, thecombined effect of the main locking system having a small angle, and thespring loaded core wedges transferring the clamp force of the machine toachieve concentricity, provide a considerable improvement over prior artdesigns, as mold breathing ceases to have an effect on the centering ofmold halves or the wall thickness of the molded part. Furthermore, assoon as the mold starts to open, the spring-loaded pucks 34 release andpull core wedges 20 away from cavity wedges 22, thus preventing gallingof these items. The larger angle of protrusions 28 and pucks 34 againstcavity wedges 30 allows for quick release of the effect of clampingforces on wedges 20 and 22.

As can be seen in FIG. 2, the example embodiment of the invention showsa pair of pucks 34 for each core wedge 20, but it should be understoodthat a larger number of pucks could be employed if desired, spacepermitting. Similarly, a single puck 34 could be used for each corewedge 20. While a pair of pucks 34 on each core wedge has somefunctionality advantages, a design with a single puck per core wedgecould be utilized as a more economical alternative or for othersituations, such as when space is restricted.

Further variations of the main embodiment of the invention are describedbelow.

An alternate design as shown in FIG. 7 provides a network of greasegrooves 40 on the active surfaces of cavity wedges 22. A supply system42, attached to the outer surface of the mold, delivers the correctamount of grease via internal channels, through holes 44 of cavitywedges 22 to the network of grooves, to improve contact between cavitywedges 22 and core wedges 20 and further prevent wear on the 0°-3°taper.

A detail of the wedge lock system of FIG. 4 is shown in FIGS. 8A and 8B.FIG. 8A presents a gap-free design, where both core protrusions 28 andspring-loaded pucks 34 are in contact with cavity wedges 30 when mold isclosed. FIG. 8B presents a design with gap, where only the spring-loadedpucks 34 are in contact with cavity wedges 30 when mold is closed, thetapered surfaces of core protrusions 28 being below the front surfacesof spring-loaded pucks 34.

A version of an alternate embodiment is shown in part FIG. 4B anddescribed herein, in which a forward protrusion (130) in the core blockas shown (or alternately the cavity block) mates with a correspondingopening in the opposite block, said protrusion having a first angledlateral side and an opposite angled lateral side. The first oppositeblock portion, situated opposite said first angled lateral side of theprotrusion has a mating surface to the first angled side of theprotrusion. The second opposite block portion is situated opposite saidsecond angled lateral side and in said closed position, said first andsecond opposite block portions engage the respective first and secondangled sides of the protrusions, thereby creating increased clampingforce in the closed position. As shown in FIG. 4B, the opposite block isthe cavity block and cavity wedges are secured to the first and secondcavity block portions. If cavity wedges are present, they have matingsurfaces to the angled sides of the protrusion (or if desired, such asshown, a protrusion wedge shown on one side as item 120 or protrusionwedges on both sides of the protrusion may be utilized). If protrusionwedges are utilized, the sides of the protrusion itself may or may notbe angled and said cavity wedges engage the angled sides of theprotrusion wedges. The angled sides of the protrusion or if presentprotrusion wedges attached to the protrusion are typically angled eachangled at a range of 0° to 30° to said direction of mold movement, butmay be even greater an angle.

An alternate embodiment is presented in FIG. 9. The design is similar tothat of FIG. 8A, in that the core wedge 20′ is activated transversallyby spring-loaded pucks 34′, but this embodiment has no taper on theactive surfaces of the core and cavity wedges, the relative motionbetween them being allowed by a set of roller bearings 46 inserted inthe active face of the core wedge 20′ (and prevented from accidentalremoval by a slotted cover plate 48). When the mold opens, thespring-loaded pucks 34′ move the core wedges 20′ (complete with rollerbearings 46 and cover plate 48) away from the center of the mold (awayfrom cavity wedges 22′ and out of contact with these). As the moldcloses, cavity wedges 30′ urge pucks 34′ into their pockets in coreprotrusions 28′, and the compressed spring washers 38′ urge the corewedges 20′ with roller bearings 46 into contact with cavity wedges 22′,the roller bearings 46 guiding the relative travel between wedges untilthe mold is completely closed.

The embodiment of the invention (as presented in FIGS. 8A and 8B) andthe alternate embodiment of FIG. 9 both present a core wedge designactivated by springs to float in a transversal direction (along the axisof the spring-loaded pucks 34, 34′).

An alternate embodiment in accordance with the invention, as shown inFIG. 10, presents a core wedge 20″ floating axially (i.e. parallel tothe centerline of the injection mold), as will be explained in moredetail below. As shown in FIG. 10, core wedge 20″, attached to coreblock 12″ with shoulder bolts 50, is activated axially by springs 52.This design also allows for larger tapers on the active faces of corewedges 20″ and cavity wedges 22″, with the advantage that it achievesimmediate release of contact when mold opens. The presence of cavitywedges 30″ is not mandatory in this design, as the pair of core wedges20″ and cavity wedges 22″ achieves the desired degree of centeringaccuracy. When the mold opens, springs 52 extend core wedges 20″ axiallyaway from core block 12″, until they bottom out against heads ofshoulder bolts 50. To prevent friction wear or seizing of the corewedges 20″ against the core block 12″, protrusions 28″ of core block 12″are provided with wear plates 54, made of a material with lowcoefficient of friction, which allow axial travel of core wedges 20″with minimal surface wear.

Another alternate embodiment is presented in FIG. 10. The design issimilar to that of FIG. 8A, in that the core wedge 20″ is activatedtransversally by spring-loaded pucks 34″, but this embodiment has notaper on the active faces of the core and cavity wedges, the relativemotion between them being allowed by a set of roller bearings 52inserted in the active face of the core wedge 20″ (and prevented fromaccidental removal by a slotted cover plate 54). When the mold opens,the spring-loaded pucks 34″ move the core wedge 20″ (complete withroller bearings 52 and cover plate 54) towards the center of the mold(towards the cavity wedge 22″). As the mold closes, a lead-in taper 56of the cavity wedge 22″ will start pushing the extended core wedge 20″back into place, and the roller bearings 52 take over right after,guiding the relative travel until the mold is completely closed.

While spring washers (Belleville type) are illustrated as means ofcompression to activate the pucks to provide continuous contact betweenthe sets of wedges, it should be understood that any type of technologythat achieves compression could be used, such as compressible bumpers(urethane or other non-metallic compounds), as well as other means suchas gas springs.

As well, it should be understood that the floating assembly (pucks,springs, shoulder bolts and wedges), which was presented as part of thecore half of the mold, could alternately be reversed and designed aspart of the cavity half of the mold. In such case, the positioning ofall of the components of the system would be reversed between the coreand cavity side.

Furthermore, with regards to the plan views of the mold halves, inaccordance with an aspect of the invention, wedges may be located at45°, 135°, 225° and 315° (as shown in FIG. 2, 3, and spatially in FIGS.6 and 7), but they could alternately be placed at quadrants (i.e., at0°, 90°, 180°, and 270°) without any changes to mold behaviour. It isalso contemplated that more or less than 4 wedge sets, spaced around thecentral axis of the mold could be utilized in accordance with an aspectof the invention.

It should be further understood that the mold may include bottom 10 andtop 16 plates or alternately may have solid core and cavity blockswithout backing plates, such as bottom 10 and top 16 plates). Thefunction of the wedge lock system of the invention herein would notimpacted by the presence or absence of such backing plates in the mold.In fact, some of the figures show an embodiment with backing plates(such as bottom plate 10 and top plates 16 shown in FIG. 4) and someshow solid core and cavity blocks (such as in FIG. 4A). It should beunderstood that many changes, modifications, variations and other usesand applications will become apparent to those skilled in the art afterconsidering the specification and the accompanying drawings. Forexample, each said core wedge assembly and cavity wedge may be made ofhigh hardened low friction steel material or non ferrous low frictionmaterial, or other suitable material, not specifically described.

Therefore, any and all such changes, modifications, variations and otheruses and applications which do not depart from the spirit and the scopeof the invention are deemed to be covered by the invention. Accordingly,the invention should be understood to be limited only by the claimsappended hereto, purposively construed.

1. A wedge lock system for injection molds comprising a mating coreblock and cavity block which move between an open position and closedposition, and in said closed position molten plastic may be injectedbetween the faces of said core and cavity blocks to form a plasticinjection mold product, said wedge lock system comprising: a forwardprotrusion in the core block which mates with a corresponding opening inthe cavity block, said protrusion having a first lateral side and anopposite angled lateral side; a first cavity wedge, secured to thecavity block, situated opposite said first lateral side; a core wedgeassembly including a core wedge piece positioned adjacent the first sideof the protrusion and being connected by compressible attachment meanswhich extends laterally through said protrusion to at least one floatingpuck, said at least one puck extending laterally outwardly from saidangled side of the protrusion; a second cavity wedge secured to thecavity block having a mating angled surface to the angled side of theprotrusion, which in said closed position, engages the angled side ofsaid protrusion and urges said laterally outwardly extending at leastone floating puck inwardly to compress said compressible attachmentmeans and thereby urge said core wedge piece into firm contact with saidfirst cavity wedge.
 2. A wedge lock system for injection moldscomprising a mating core block and cavity block which move between anopen position and closed position, and in said closed position moltenplastic may be injected between the faces of said core and cavity blocksto form a plastic injection mold product, said wedge lock systemcomprising: a wedge compressibly mounted to the face of said core blockor cavity block, biased in a floating position away from said block,said wedge having an angled surface to the direction of movement of themold machine, said wedge being compressed against said block as theangled surface of the wedge comes into engagement with a mating angledsurface of a wedge secured to the opposite side of the mold (or with amating angled surface of the opposite side of the mold directly), as themold approaches the closed position thereby providing enhanced clampingforce in the closed position during plastic injection.
 3. A wedge locksystem as recited in claim 1, wherein said first side of the protrusionand the mating side of core wedge piece are oriented parallel to thedirection of movement of the mold between an open and closed position.4. A wedge lock system as recited in claim 1 wherein the angled side ofprotrusion has an angled surface to the said direction of mold movementof 3° to 20°.
 5. A wedge lock system as recited in claim 1 wherein theinterface between the core wedge piece and first cavity wedge has anangle to the direction of mold movement of no greater than 3°.
 6. Awedge lock system as recited in claim 1 wherein said compression meansis selected from the group consisting of: a compressible coil spring,washer spring, bumper, gas spring.
 7. A wedge lock system as recited inclaim 1 wherein each said core wedge assembly includes a pair offloating pucks attached to said core wedge assembly extending throughsaid protrusion.
 8. A wedge lock system as recited in claim 1 whereinthe interface between the core wedge piece and cavity wedge includes anetwork of grease grooves on either of said cavity wedge or core wedgepiece, said grooves receiving an amount of grease, delivered by deliverymeans to further prevent wear on the interface between said core wedgeand cavity wedge.
 9. A wedge lock system as recited in claim 1 whereinthe interface between the core wedge piece and cavity wedge includes aset of roller bearings, guiding the relative travel between wedges asthe mold moves between closed and open positions.
 10. A wedge locksystem as recited in claim 9 wherein said roller bearings are insertedin the core wedge piece or cavity wedge and prevented from accidentalremoval by a slotted cover plate.
 11. A wedge lock system for injectionmolds comprising a mating core block and cavity block which move betweenan open position and closed position, and in said closed position moltenplastic may be injected between the faces of said core and cavity blocksto form a plastic injection mold product, said wedge lock systemcomprising: a forward protrusion in the cavity block which mates with acorresponding opening in the core block in said closed position, saidprotrusion having a first lateral side and an opposite angled lateralside; a first core wedge, secured to the core block; a cavity wedgeassembly including a cavity wedge piece positioned adjacent the firstside of the protrusion and being connected by compressible attachmentmeans which extends laterally through said protrusion to at least onefloating puck, said at least one puck extending laterally outwardly fromsaid angled side of the protrusion; a second core wedge secured to thecore block having a mating angled surface to the angled side of theprotrusion, which in said closed position, engages the angled side ofsaid protrusion and urges said laterally outwardly extending at leastone floating puck inwardly to compress said compressable attachmentmeans and thereby urge said cavity wedge piece into firm contact withsaid first core wedge.
 12. An injection mold comprising a mating coreblock and cavity block which move between an open position and closedposition, and in said closed position molten plastic may be injectedbetween the faces of said core and cavity blocks to form a plasticinjection mold product, including a plurality of wedge lock systems ofclaim 1, each equidistantly spaced around a central axis of the molddefined along the direction of movement of the mold at regularintervals.
 13. An injection mold as recited in claim 12 wherein 4 saidwedge lock systems are spaced equidistantly around the central axis at90° intervals.
 14. An injection mold as recited in claim 12 wherein 8said wedge lock systems are spaced equidistantly around the central axisat 45° intervals.
 15. An injection mold comprising a mating core blockand cavity block which move between an open position and closedposition, and whilst in closing motion, molten plastic may be injectedbetween the faces of said core and cavity blocks to form a plasticinjection mold product, including a plurality of regularly spaced wedgelock systems of claim
 12. 16. A wedge lock system as recited in claim 1wherein each said core wedge assembly and cavity wedge are made of highhardened low friction steel material or non ferrous low frictionmaterial.
 17. A wedge lock system for injection molds comprising amating core block and cavity block which move between an open positionand closed position, and in said closed position molten plastic may beinjected between the faces of said core and cavity blocks to form aplastic injection mold product, said wedge lock system comprising: aforward protrusion in the core block (or cavity block) which mates witha corresponding opening in the opposite block, said protrusion having afirst angled lateral side and an opposite angled lateral side; a firstopposite block portion, situated opposite said first angled lateral sideof the protrusion having a mating surface to the first angled side ofthe protrusion; a second opposite block portion, situated opposite saidsecond angled lateral side, wherein, in said closed position, said firstand second opposite block portions engage the respective first andsecond angled sides of the protrusions, thereby creating increasedclamping force in the closed position.
 18. A wedge lock system asrecited in claim 17, wherein said opposite block is the cavity block andcavity wedges are secured to one or both of the cavity block portions,said cavity wedges having mating surfaces to the angled sides of theprotrusion and said cavity wedges engage the angled sides of theprotrusions.
 19. A wedge lock system as recited in claim 17 furthercomprising protrusion wedges attached to each of the first and oppositeangled lateral sides of the protrusion which engage the respectiveopposite block portion in the closed position.
 20. A wedge lock systemas recited in claim 17 wherein the angled sides of the protrusion (orattached protrusion wedges) are each angled at 0° to 30° to saiddirection of mold movement.